With increasing industrial development, diverse electronic devices are used to achieve various purposes. An electronic device comprises a plurality of electronic components. Generally, different kinds of electronic components are operated by using different voltages.
As known, a power supply is essential for many electronic devices such as personal computers, industrial computers, servers, communication products or network products. Usually, the user may simply plug a connector of a power supply into an AC wall outlet commonly found in most homes or offices so as to receive an AC voltage. The power supply will convert the AC voltage into a regulated DC output voltage for powering the electronic device. The regulated DC output voltage is transmitted to the electronic device through a power cable.
FIG. 1 is a schematic block diagram illustrating the connection between a power supply and a system circuit of an electronic device according to the prior art. As shown in FIG. 1, the power supply 11 includes a power converting circuit 111 and an input capacitor Cx. The input capacitor Cx is connected to the input terminal of the power converting circuit 111 for suppressing electromagnetic interference (EMI). The output terminal of the power converting circuit 111 is connected to the system circuit 12. By the power converting circuit 111, the electric energy of an input voltage Vin is received and converted into an output voltage Vo for powering the system circuit 12. If the input voltage Vin is suffered from sudden interruption, the power converting circuit 111 fails to continuously provide the output voltage Vo to the system circuit 12. If no proper measures (for example saving the game's progress of a game console, saving the operating data of the computer and reducing the bulb temperature of a projector) are taken before the electronic device 1 is turned off, some important data stored in the electronic device 1 are possibly lost and the electronic device 1 fails to be normally turned on or normally operated again. In other words, a prerequisite procedure should be done before the electronic device 1 is turned off.
For providing a sufficient time period to perform the prerequisite procedure, an input voltage detecting circuit is used to detect the magnitude of the input voltage Vin. If the input voltage Vin is suffered from interruption, the input voltage detecting circuit will issue a power status signal. According to the power status signal, the electronic device 1 performs the prerequisite procedure.
FIG. 2 is a timing waveform diagram schematically illustrating the corresponding voltage signals processed in a conventional input voltage detecting circuit. In a case that the input voltage Vin is suffered from interruption at the first time spot t1, the discharging period of the input capacitor Cx is too long and the magnitude of the input voltage Vin is decreased at a slow rate, because the capacitance value of the input capacitor Cx and the impedance at the input terminal of the power converting circuit 111 are very large. In addition, since the conventional input voltage detecting circuit (not shown) is very simple, its response to the interruption of the input voltage Vin is very slow. Until the magnitude of the input voltage Vin is lowered than a reference voltage at the second time spot t2, the conventional input voltage detecting circuit may discriminate that the input voltage Vin is suffered from interruption. At the same time, a power status signal Vk generated by the input voltage detecting circuit is at a high-level status, meaning that the input voltage Vin is interrupted.
Since the power status signal Vk indicative of interruption of the input voltage Vin is generated after the input voltage Vin has been suffered from interruption for a delaying time Td, the user fails to realize the timing of performing the prerequisite procedure before the electronic device 1 is turned off. In other words, the conventional input voltage detecting circuit is not feasible to the power supply 11.
There is a need of providing an improved input voltage detecting circuit so as to obviate the drawbacks encountered from the prior art.